A conventional vertical NAND string uses an aluminum oxide (Al oxide) etch-stop layer for stopping a high-aspect-ratio pillar (trench) etch. Because the Al oxide etch-stop layer does not have sufficient etch selectivity, a relatively thicker layer of the Al oxide is needed in order to be able to control stopping of the etch. The relatively thicker Al oxide layer causes an undesirably longer channel distance between the select gate (SG) and the first wordline (WL) of the NAND string, thereby underutilizing the full length of the NAND string channel. Additionally, the typical wet-etch cleanse chemicals, such as Hydrofluoric (HF) acid, Buffered Oxide Etch (BOE) chemistry and phosphoric acid, used for an Al oxide fast etch to clean the dry etch polymers, easily etch the Al oxide and cause a recess in the side wall of the channel at the Al oxide layer that forms an undesirable floating gate (FG), and results in an on-current degradation for the NAND string.
It will be appreciated that for simplicity and/or clarity of illustration, elements depicted in the figures have not necessarily been drawn to scale. For example, the dimensions of some of the elements may be exaggerated relative to other elements for clarity. The scaling of the figures does not represent precise dimensions and/or dimensional ratios of the various elements depicted herein. Further, if considered appropriate, reference numerals have been repeated among the figures to indicate corresponding and/or analogous elements.